This invention relates in general to a display device containing a light shutter front end unit to modulate light transmittance and a gas discharge back end unit supplying light of one or more colors to the front end unit.
As portable computers become more popular, flat panel display technology becomes more and more important. The most successful flat panel display technology today are the liquid crystal display (LCD) panels. In the current commercial color LCD display panels, color filters are used to filter white light into the three primary colors. In addition, in order to obtain the desired color mixing ratio, each of the monochrome pixel will need to be partitioned into three subpixels in order to modulate the transmittance of each of the three primary colors. In this approach, most of the light generated by the back end unit is lost in the color filter. The opening in the LCD panel which allows the light to pass through is also reduced since more area is occupied by signal paths and various devices necessary to control the three subpixels. Multiplying these two factors together, color filtered LCD panels become quite power inefficient. Generally, high power consumption and high price, both caused by the complexity introduced by the color filter and the significantly increased pixel density, are considered as the two most serious drawbacks of current color LCD products.
In the above-referenced PCT patent application Ser. No. PCT/US92/10925, filed Dec. 18, 1992, an alternative method for generating color images with LCD is proposed. In this approach, a new backlight structure called electronic fluorescent backlight (EFBL) is used to produce color light pulses of the three primary colors. When these color light pulses are generated in synchronization with the LCD scanning operation, in a manner similar to that described below as indicated in FIG. 2, and when such color light pulses pass through the LCD pixels when the illuminated pixel has substantially finished the transition, good quality color image is produced. Since the EFBL can generate highly saturated red, green and blue primary colors, there is no need for color filtering. The LCD only needs to modulate the transmittance of the three color pulses to produce the desired color mixing. This approach allows the light generated by the backlight unit to pass through the LCD without being filtered. This approach not only avoids the complexity and cost of color filter and the associated subpixels, but also vastly improves the light transmittance of the LCD at the same time.
The EFBL in the related applications are cathode luminescence devices. Due to the light emission principle of these devices, an anode voltage of 5 KV or higher is frequently desirable or necessary in order to produce light at sufficiently high efficiency levels. Due to insulation and other electrical reliability considerations, this high anode voltage puts constraint both on the thickness of the device and on the size of the anode power supply. As portable computers become more and more compact, this size restriction may become a serious deficiency. Moreover, the high anode voltage can easily become a safety hazard in the compact packaging of a portable system. The handling of this high voltage would require extra effort of the system designer and may potentially increase the cost of the system. It is thus desirable to provide an improved display device where the above described difficulties are overcome.